Friction-reducing drill pipe component

ABSTRACT

The friction-reducing drill pipe component in the form of a sub ( 10 ) is adapted to form part of a drill string. The sub ( 10 ) comprises a tubular mandrel ( 12 ) having first and second ends for connection to adjacent components of the drill string. A sleeve ( 18 ) is mounted on the mandrel ( 12 ), and first and second stops on the mandrel ( 16, 20 ) restrain the sleeve ( 18 ) against axial movement relative to the mandrel ( 12 ). One of the stops ( 20 ) is removable or retractable to permit the sleeve ( 18 ) to be removed over the first end of the mandrel.

[0001] This invention relates to a drill pipe component, and inparticular to a component to be placed in a string of drill pipe toreduce the friction between the string and the hole wall.

[0002] In industries where long holes or bores are drilled, such as theoil and gas exploration and extraction industries, the friction whichoccurs due to contact between the drill string and the bore wall mayresult in a substantial increase in the torque required to rotate thestring and the drill bit. Such contact also causes wear and damage tothe steel casing used to line sections of the bore.

[0003] In an effort to avoid these difficulties there have been variousproposals for friction reducing components to be mounted in or on thestring. U.S. Pat. No. 5,261,498 (The Red Baron (Oil Tools Rental)Limited) describes a typical friction reducing component or sub, inwhich a bore wall contacting sleeve is mounted on the lower part of amandrel via bearings and is axially retained on the lower mandrel partbetween a shoulder and an upper mandrel part. While this and other subshave been used successfully in numerous operations, the cost andcomplexity of such subs has limited their widespread adoption and use.

[0004] It is among the objects of embodiments of the present inventionto provide a friction-reducing drill pipe component which is relativelysimple in construction and is thus less expensive to manufacture andmaintain.

[0005] According to the present invention there is provided afriction-reducing drill pipe component for forming part of a drillstring, the component comprising a tubular mandrel having first andsecond ends for connection to adjacent components of the drill string, asleeve mounted on the mandrel, and first and second stops on the mandrelfor restraining the sleeve against axial movement relative to themandrel, at least the first stop being removable from the mandrel topermit the sleeve to be removed over the first end of the mandrel.

[0006] In use, the major parts of the component may be disassembledsimply by removing the first stop and then lifting the sleeve over thefirst end of the mandrel. This contrasts with conventional arrangementsin which removal of the sleeve, if possible, requires, for example, thedismantling of the mandrel or heat treatment and expansion of thesleeve. Thus, maintenance and repair of components made in accordancewith embodiments of the present invention is relatively simple and inmany instances may be carried out on-site at a drilling location.

[0007] The sleeve may be rotatable relative to the mandrel or may benon-rotatable on the mandrel. In this area, components or subs in whichthe sleeve is fixed relative to a mandrel are described as “rotating”subs, as the sleeve rotates in the bore with the drill string. If thesleeve is rotatable on the mandrel such subs are described as“non-rotating” subs, as the sleeve remains stationary relative to thebore.

[0008] In non-rotating subs, bearings may be provided between the sleeveand mandrel, or the sleeve and mandrel may define bearing surfaces.Where bearings are provided these may be introduced into the gap betweenthe sleeve and the mandrel through a port in the sleeve. Bearinglubricant may be trapped between the mandrel and sleeve, however it ispreferred that the fluid in the bore provides the necessary lubrication,and to this end the spacing of the stops may be selected to provide aflow path between the stops and the sleeve ends. One of the upper stopand the upper end of the sleeve may be configured to permit flow offluid therebetween in the event that the contact between the sleeve andbore wall causes the sleeve to be pushed upwardly into contact with theupper stop, for example the upper end of the sleeve or the stop may bescalloped. Alternatively, ports may be provided in the upper end of thesleeve.

[0009] Preferably, the first stop is in the form of a collar. The collarmay engage with a screw thread formed on the mandrel or may be retainedon the mandrel by releasable connectors. The releasable connectors maybe in the form of bolts or pins or, most preferably, are in the form ofsprung pins or dogs which normally extend radially from the mandrel toengage and retain the collar. The collar may define ports therethroughto allow the dogs to be pushed inwardly to allow removal of the collar.The collar may also define slots in communication with the ports so thatthe collar may be rotated to cover the pins. Where sprung dogs areutilised to retain the sleeve, the dogs may be pushed inwardly to permitremoval of the sleeve. Thus, with this embodiment of the invention it ispossible for unskilled personnel to remove and replace the sleeve usingonly very simple tools, such that components may be repaired on-sitewithout requiring specialised assistance or equipment.

[0010] Preferably also, the second stop is in the form of a stop ring.The ring may be removable but is preferably integral with the mandrel.In the preferred embodiment the mandrel, the mandrel end connections andthe second stop are machined from a single piece of metal. The firststop and the sleeve may each also be formed of single pieces of metal.Accordingly, the resulting connector has only a small number of partsand is therefore easily assembled and disassembled and may be of robustconstruction.

[0011] The sleeve may have a cylindrical outer surface, or may defineaxial or helical blades with slots therebetween, to facilitate passageof drilling fluid through the annulus between the drill string and thebore wall. The blades may be of resilient material, such as PTFE, PEEKpolymeric material, or vulcanised neoprene, most preferably reinforcedwith metal or some other rigid structure. Alternatively, the blades maybe of metal, such as steel or alloy. The metal blades may be integralwith the sleeve or welded or otherwise bonded to the sleeve. The slotsmay be undercut.

[0012] According to another aspect of the present invention there isprovided a friction-reducing drill pipe component for forming part of adrill string, the component comprising a tubular mandrel having firstand second ends for connection to adjacent components of the drillstring, and a sleeve mounted on the mandrel, the sleeve definingexternal blades with undercut channels therebetween.

[0013] According to a further aspect of the present invention there isprovided a friction-reducing drill pipe component for forming part of adrill string, the component comprising a tubular mandrel having firstand second ends for connection to adjacent components of the drillstring, a sleeve mounted on the mandrel, and spring-mounted lock dogsmounted on the mandrel and operatively associated with the sleeve forreleasably retaining the sleeve on the mandrel.

[0014] These and other aspects of the present invention will now bedescribed, by way of example, with reference to the accompanyingdrawings, in which:

[0015]FIG. 1 is a part-sectional view of a friction-reducing drill pipecomponent in accordance with a first embodiment of the presentinvention;

[0016]FIG. 2 is a part-sectional view of a friction-reducing drill pipecomponent in accordance with a second embodiment of the presentinvention;

[0017]FIG. 3 is a sectional view of the mandrel of the component of FIG.2;

[0018]FIG. 4 is a sectional view on line 4-4 of FIG. 2;

[0019]FIG. 5 is a part-sectional view of a friction-reducing drill pipecomponent in accordance with another embodiment of the presentinvention;

[0020]FIG. 6 is a sectional view of the mandrel of the component of FIG.5;

[0021]FIG. 7 is a perspective view of the sleeve of the component ofFIG. 5; and

[0022]FIG. 8 is a perspective view of an alternative sleeve for thecomponent of FIG. 5.

[0023] Reference is first made to FIG. 1 of the drawings, whichillustrates a friction-reducing drill pipe component in the form of asub 10 forming part of a drill string (not shown) for location in adrilled bore. The sub 10 comprises a tubular body or mandrel 12 providedwith conventional conical threaded pin and box connections 14, 15 topermit the sub 10 to form part of a drill string. A stop ring 16 isformed on the mandrel 12 and locates the lower end of a sleeve 18. Theupper end of the sleeve 18 is located by a stop comprising a set ofsprung lock dogs 20 biassed to extend radially from the mandrel 12 intocorresponding slots 22 defined on the inner surface of the sleeve 18. Inthis embodiment the sleeve is a “rotating” sleeve, in that it rotateswith the mandrel 12.

[0024] To remove the sleeve 18 from the mandrel 12 an operator depressesthe lock dogs 20 by pushing on the lock dogs 20 through the sleeve ports24 which communicate with the slots 22. When the lock dogs 20 are pushedinwardly the sleeve 18 may be lifted over the depressed dogs 20, andremoved from the end of the mandrel.

[0025] Reference is now made to FIGS. 2, 3 and 4 of the drawings, whichillustrate a friction-reducing pipe component in the form of a sub 30 inaccordance with a further embodiment of the present invention. The sub30 is somewhat similar to the sub 10 described above, in that itcomprises a tubular mandrel 32 defining corresponding pin and boxconnections 34, 35 and carrying a stop ring 36 to retain a sleeve 38 onthe mandrel 12. Further, the upper end of the sleeve 38 is retained bylock dogs 40. However, the lock dogs 40 engage with a lock collar 41rather than with the sleeve 38, which is thus free to rotate on themandrel 32. Those working in the area would describe the sleeve 38 as ofthe “non-rotating” type, as in use the sleeve 38 remains stationaryrelative to the bore wall, while the mandrel 32 and the remainder of thedrill string rotates.

[0026] The lock dogs 40 engage slots 42 in the collar 41, and ports 44provide operator access to the lock dogs 40. Each port 44 is located atone end of the respective slot 42, such that the collar 41 may berotated on the mandrel 32 until the dogs 40 engage the other “closed”end of the slot 42. Of course the ports 44 and slots 42 are arrangedsuch that rotation of the sub 30 in a bore tends to result in rotationof the collar 41 to bring the dogs 40 to the closed ends of the slots42.

[0027] The lock dogs 40 are illustrated in greater detail in FIG. 4 ofthe drawings. Each lock dog 40 is located in a respective threaded hole46 which accommodates a stepped and threaded lock dog retainer 48. Alarger diameter stop 50 is provided on each lock dog 40 to engage aretainer shoulder 52 and limit the outward radial extension of the dog40. A compression spring is provided between each lock dog and the baseof the hole 46, to urge the dog radially outwardly. The dogs 40 areported to prevent the dogs being pushed inwardly by the elevatedpressures experienced downhole.

[0028] In use, a number of subs 30 will be provided in a drill string,and as the string is rotated in a bore the sleeve 38, which is of largerdiameter than the other parts of the drill string, will contact thecasing which lines the bore and the mandrel 32 will rotate relative tothe non-rotating sleeve 38. In this particular embodiment the mandrel 32and the sleeve 38 each define plane bearing surfaces, howeverlubrication is provided by the drilling mud which, during a drillingoperation, will flow upwardly through the annulus between the sub 30 andthe bore casing. This drilling mud will find its way between the stopring 36 and the lower end of the sleeve 38, pass between the mandrel andthe sleeve, and then flow out between the upper end of the sleeve 38 andthe collar 41. To ensure that the fluid may flow out between the upperend of the sleeve 38 and the collar 41, the collar 41 is scalloped.

[0029] From FIG. 3 of the drawings it will be noted that the mandrel 32and stop ring 36 are formed from a single piece of metal. Further, thesleeve 38 and collar 41 are also each formed of a single piece of metal.The sub 30 is therefore very robust, and tests have revealed that thevarious parts of the sub 30 experience very little wear under normalcircumstances. However, if it is desired to remove the sleeve 38 fromthe mandrel 32, this is achieved by depressing the lock dogs 40 to allowremoval of the collar 41, and then depressing the lock dogs to allowremoval of the sleeve 38 from the end of the mandrel. Similarly, thesleeve 38 may be refitted on the mandrel 32 with equal ease.

[0030] Reference is now made to FIGS. 5, 6 and 7 of the drawings whichillustrate a friction-reducing drill pipe component in the form of a sub60 in accordance with a further embodiment of the present invention. Thesub comprises a tubular mandrel 62 provided with conventional pin andbox connections 64, 65 to permit the sub 60 to form part of a drillstring. The mandrel also defines a stop ring 66 which locates the lowerend of a sleeve 68, the upper end of the sleeve 68 being located by acollar 70 which engages a thread 72 cut on the outer surface of themandrel 62. Like the sub 30 described above, the sleeve 68 is rotatableon the mandrel 62, and in this embodiment various bearings 74 areprovided between the sleeve 68 and the mandrel 62, the opposing faces ofwhich are shaped to define appropriate bearing races or tracks 76, 77(it should be noted that the dimensions of the bearings 74 and thetracks, 76, 77 are shown somewhat exaggerated in the Figures).

[0031] Reference is now made in particular to FIG. 7 of the drawings,which illustrates the sleeve 68. It will be noted that the sleeve 68defines four axially extending blades 78 with channels or slots 80therebetween. The blades 78 are formed of steel, a metal alloy or aresilient material, such as PTFE, moulded or otherwise formed or securedaround a steel reinforcing body. To facilitate assembly and disassemblyof the sub 60, various ports 82 are provided in the sleeve 68 to allowbearings to be placed in or removed from the appropriate bearing tracks76, 77 between the mandrel 62 and the sleeve 68.

[0032] To disassemble the sub 60, the ports 82 are opened and thebearings 74 removed therethrough. The collar 70 is then disengaged fromthe thread 72 and removed from the mandrel 62. The sleeve 68 may then belifted over the upper end of the mandrel 62. To reassemble the sub 60these steps are simply repeated in the reverse order.

[0033] Reference is now also made to FIG. 8 of the drawings, whichillustrates an alternative sleeve 88 defining three helically extendingblades 90 with undercut channels 92 extending therebetween; the undercutchannels 92 provide a larger flow area between the blades 90 while notreducing the contact area provided by the blades 90.

[0034] It will be clear to those of skill in the art that theabove-described embodiments are merely exemplary of the presentinvention, and that various modifications and improvements may be madethereto, without departing from the scope of the present invention. In afurther embodiment, the sub 30 described above may be modified by theprovision of a sleeve defining a series of blades, and in a stillfurther embodiment the sleeve may include means to permit for filling ofthe gap between the sleeve 38 and the mandrel 32 with bearings, whichmay be in the form of a large number of glass balls.

1. A friction-reducing drill pipe component for forming part of a drillstring, the component comprising a tubular mandrel having first andsecond ends for connection to adjacent components of the drill string, asleeve mounted on the mandrel, and first and second stops on themandrel, intermediate the first and second ends, for restraining thesleeve against axial movement relative to the mandrel, at least thefirst stop being removable or retractable to permit the sleeve to beremoved over the first end of the mandrel.
 2. The component of claim 1,wherein the sleeve is rotatable relative to the mandrel.
 3. Thecomponent of claim 2, wherein the sleeve and mandrel define bearingsurfaces.
 4. The component of claim 2, wherein bearings are providedbetween the sleeve and mandrel.
 5. The component of claim 4, wherein thebearings are introduced into a gap between the sleeve and the mandrelthrough a port in the sleeve.
 6. The component of any of claims 2 to 5,wherein one or more openings are provided in or between the sleeve andmandrel to permit drilling fluid in the bore to enter a gap between thesleeve and mandrel and serve as a lubricant therebetween.
 7. Thecomponent of claim 6, wherein the spacing of the stops and the length ofthe sleeve is selected to provide a flow path between the stops and thesleeve ends.
 8. The component of claim 7, wherein one of an upper stopand an upper end of the sleeve is configured to permit flow of fluidtherebetween in the event that the contact between the sleeve and borewall and downward movement of the drill string relative to the bore wallcauses the sleeve to be pushed upwardly into contact with the upperstop.
 9. The component of claim 8, wherein the upper end stop isscalloped.
 10. The component of any of the preceding claims wherein thefirst stop is in the form of a collar.
 11. The component of claim 10,wherein the collar engages a screw thread formed on the mandrel.
 12. Thecomponent of claim 10, wherein the collar is retained on the mandrel byreleasable or retractable connectors.
 13. The component of claim 12,wherein the connectors are sprung dogs which normally extend radiallyfrom the mandrel to engage and retain the collar.
 14. The component ofclaims 12 or 13, wherein the collar defines ports therethrough to permitaccess to the connectors.
 15. The component of claim 14, wherein thecollar also defines slots in communication with the ports so that thecollar may be rotated to cover the connectors.
 16. The component of anyof the preceding claims, wherein the second stop is in the form of astop ring.
 17. The component of claim 16, wherein the ring is integralwith the mandrel.
 18. The component of claim 17, wherein the mandrel,the mandrel end connections and the second stop are machined from asingle piece of metal.
 19. The connector of any of the preceding claimswherein the first stop and the sleeve are each formed of single piecesof metal.
 20. The connector of any of the preceding claims wherein thesleeve has a cylindrical outer surface.
 21. The connector of any ofclaims 1 to 19, wherein the sleeve carries external blades with slotstherebetween.
 22. The connector of claim 21, wherein at least the bladesurfaces are of resilient material.
 23. The connector of claim 21 or 22,wherein the slots are undercut.
 24. A friction-reducing drill pipecomponent for forming part of a drill string, the component comprising atubular mandrel having first and second ends for connection to adjacentcomponents of the drill string, a sleeve mounted on the mandrel, andspring-mounted lock dogs mounted on the mandrel and operativelyassociated with the sleeve for releasably retaining the sleeve on themandrel, the released sleeve being removable over the first end of themandrel.